Fiber reinforced composite materials are known for use in a variety of applications, including the manufacture of reinforced articles where structural strength is important. Such applications include roofing and construction materials, including artificial shingles or shakes, cables and automobile body parts. The composites used to make such articles may comprise one or more of a variety of polymeric materials as a matrix, molded together with a reinforcing fiber material, typically glass. The composites so formed are often used at high temperatures, or may otherwise be exposed to high heat conditions. Where the composites are used as building materials such as shingles or shakes, flame retardance is desirable as a safety feature. In this regard especially, some degree of resilience of the molded composites to combustion is required. Further, flammability is generally an undesirable characteristic in resin-based composites because combustion of the resin matrix typically results in release of by-products including chemical compounds and gases that are toxic to the environment and pose a safety threat if inhaled.
Accordingly, various means have been recognized in the art for improving fire resistance in molded composites. The term "fire resistance", as used herein, is intended to encompass flame retardance, i.e. the ability of the material to diminish or prevent combustion when the material is exposed to high temperatures, as well as flame suppression, or the ability of the material to extinguish flames by virtue of physico-chemical reactions that occur when it is burned.
One means of improving the fire resistance of molded composites involves coating a molded composite article with a finish that imparts fire resistance. To obtain such a finish, a coating containing the ingredient that imparts fire resistance is applied by spraying, roll coating, brushing or other means onto the surface of the already molded composite product. The obvious disadvantages of this process include the need for additional processing steps in applying and curing the fire resistant layer. Moreover, the finish is susceptible to gradual erosion or other removal over time, and therefore may not provide complete coverage of the molded surface.
An alternative means of imparting fire resistance is by addition of a flame retardant additive to the composite matrix resin before it is cured to form the composite. Adding the flame retardant additive reduces the susceptibility of the matrix resin to combustion. Research involving the development of flame retardant additives has included adding various compounds to particular resin matrices. Such compounds may provide a flame suppressant effect by virtue of physico-chemical reactions during burning. For example, compounds such as melamines or other polymeric compounds may release flame suppressant compounds such as halogenated gases, upon combustion. Further, this type of chemical flame suppressant additive may optionally be combined with a synergist such as, for example, various oxides of antimony and arsenic. Alternatively, an inert, non-reactive, non-combustible flame retardant material may be added as a filler. Such a material may be one that is highly resistant to thermal degradation, and does not burn at temperatures that would cause combustion, or may otherwise provide a cooling effect. One such additive is a finely divided silica which may absorb heat at high temperatures.
While chemical flame retardant additives have been known in the art, it has been recognized that the selection of a particular additive is determined by the resin that is used to form the composite matrix. For example, U.S. Pat. No. 5,357,026 points out that particular flame retardant additives are specific to particular matrix resins. Therefore, significant experimentation is required to identify effective flame retardant additives and amounts thereof that may be used in combination with a particular matrix resin to form a fire resistant composite.
The selection of materials used to make fire resistant composites is also determined by cost. In the manufacture of such composite materials for use in the building industry, in particular, it is desirable that the costs of bulk materials used to make the composite products be maintained as low as possible, since purchasers use large quantities of these materials. Therefore, the flame retardant additive should be cost-effective to use. Availability of a cost-effective matrix resin material is also essential.
Accordingly, there exists in the art a need for a fire resistant composite wherein the desired fire resistance is provided by the addition of a flame retardant additive that can be cost-effectively used with a compatible matrix resin.